Neon pink gel food colorsuch as Betty Crocker brand
7oz.jar marshmallow cream
7oz.sweetened flaked coconut
Preheat oven to 350 degrees. Grease a 2 quart heat-proof stainless steel bowl with shortening and lightly flour, or coat with flour-based baking spray (such as Baker’s Joy). Set aside.
Whisk together cocoa and hot water. In a separate bowl, whisk together flour, baking soda, baking powder, and salt. Melt butter with sugar in a saucepan over medium-low heat, stirring to combine. Remove from heat, and pour mixture into a mixing bowl. Beat with an electric hand mixer until mixture has cooled enough to add the eggs without scrambling them. Add eggs, vanilla, and then cocoa mixture. Beat until well combined.
Reduce mixer speed and add flour mixture in two batches, alternating with the sour cream. Pour into greased bowl and bake for 1 hour 10 minutes, or until a toothpick tester comes out clean. Let cool slightly.
Turn the cake out onto a cooling rack and let cool completely. When cool, cut the dome of the cake off about 1/3 of the way down from the top. Using a serrated knife, remove some of the interior of the cake dome by trimming it away. This will make room for the marshmallow filling.
Filling and frosting
In the bowl of a stand mixer, beat butter until fluffy. Add the confectioners’ sugar and beat until combined. Add milk or cream a little at a time until the mixture comes to spreading consistency. Add vanilla extract and a small amount of pink food color. Mix well. Transfer to a piping bag with the end snipped.
Pipe a ring of frosting around the inside of both cake pieces. Fill the hollowed center of the cake with the marshmallow cream. Sandwich the two cake pieces together, meeting the buttercream frosting at the edges. Cover the entire cake with the remaining frosting. Add extra frosting to the top of the cake and smooth into a dome shape.
In a medium bowl, tint coconut with a generous squirt of pink gel food coloring. Mix well - you can use a fork but I found my fingers did a much better job (wear gloves, if possible). Coat frosted cake with pink coconut. Cover loosely with plastic wrap and store at room temperature until ready to serve.